1. Field of the Invention
The present invention relates to a substrate for use in an apparatus for attracting a wafer such as a semiconductor wafer and a manufacturing method thereof.
2. Description of the Related Art
Electrostatic chuck are currently used to attract and hold semiconductor wafers in conveying, exposing, film-forming such as CVD (Chemical Vapor Deposition) and sputtering, micro processing, cleaning, etching or dicing the semiconductor wafers. Attention has been much paid to dense ceramics as materials for such electrostatic chucks. Particularly in the semiconductor manufacturing apparatus, a halogenated corrosive gas such as ClF.sub.3 is often used as an etching gas or a cleaning gas. It is desired that the substrate or susceptor for the electrostatic chuck has high thermal conductivity in order to rapidly heat and cool the semiconductor wafer while holding it. It is further desired that the substrate has such thermal shock resistance as to be broken due to rapid temperature change. For example, dense aluminum nitride and dense alumina are considered promising, because they have good corrosion resistance to the above-stated haloganated corrosive gas and thermal shock resistance.
In the semiconductor manufacturing apparatus, it is necessary to prevent the production of particles which would cause defects in semiconductors. In the actual semiconductor manufacturing apparatus, the semiconductor wafer is attracted and held at its back face by the electrostatic chuck. At that time, particles occur on the back surface side of the semiconductor wafer. If a large amount of particles occur, they spread over the front surface of the semiconductor wafer and into a chamber. As a result, the chamber is contaminated, so that semiconductor failure might occur on surfaces of other semiconductor wafers.
To prevent this problem, there have been proposed the following techniques. When the attracting surface of the ceramic electrostatic chuck comes in contact with a silicon wafer, the uneven attracting surface of the electrostatic chuck contacts with the silicon, and rubs off a part of the silicon having relatively low hardness to produce particles. Considering this, fine protrusions on the attracting surface of the electrostatic chuck are rounded by applying plasma onto this attracting surface, thereby preventing the silicon from being rubbed off and consequently decreasing the number of particles (Japanese Unexamined Patent Application Laid-open No. 7-245336).
According to Japanese Unexamined Patent Application Laid-open No. 8-55900, when a silicon wafer is to be attracted to the electrostatic chuck, voltage to be applied to the electrostatic chuck is gradually increased, thereby to mitigate any shock caused through the contact of the silicon wafer with the chuck. By so doing, the damage to the silicon wafer is suppressed, and the number of particles resulting from silicon wafer having been rubbed off is decreased.
The present inventors have been continuing the study to decrease the number of particles adhering to the back surface of a semiconductor wafer after the wafer has been attracted by the electrostatic chuck. According to prior art stated above, it is possible to decrease the number of particles down to for example, few to several thousands per 8-inch wafer. However, to further improve the yield of the semiconductor wafers in the semiconductor manufacturing process and to cope with more micro-structured semiconductors, it is required to decrease the number of particles furthermore. It has been desired, for example, to decrease the number of particles to a few to several hundreds per 8-inch wafer.